If you’ve ever felt the pressure of choosing the right hydraulic oil for your machinery, you’ll know all too well the minefield of information that’s out there in books or online. Instead of getting lost in the world of hydraulic fluid, hydraulic liquids or hydraulic lubricants, why not take a look at our easy-to-follow guide to hydraulic oil? It’s everything you need to know about hydraulic oils!
Hydraulic oil is available for delivery nationwide, within 24-48 hours of purchase. Give our hydraulic experts a call today on 123 .
Hydraulic oil is a non-compressible fluid that is used to transfer power within hydraulic machinery and equipment. Otherwise known as hydraulic fluid, hydraulic oil can be synthetic- or mineral-based.
At Crown Oil, as a hydraulic oil supplier, we deal with 99% of mineral-based hydraulic oils.
Although this useful fluid is commonly used in the transfer of power, hydraulic fluid can act as a sealant, coolant and lubricant within machinery and equipment.
The majority of oils which are produced are either mineral-based or synthetic. Mineral-based hydraulic oils are derived from crude oil fractions whereas synthetic hydraulic oils are made using chemically produced base fluids.
Synthetic oils can be formulated to impart superior physical properties in comparison to mineral oils, for example, high-temperature performance, biodegradability and oxidation stability.
The key role of hydraulic oil in a hydraulic system is to transfer power from one end of that system to another end through and the various hydraulic components.
When an external force is applied to the non-compressible hydraulic fluid – usually from a piston within a cylinder – the oil is pushed through the hydraulic system and ultimately produces a force on another part of the system. This results in a movement or action.
Usually applying force to material results in compression, so you may be wondering whether hydraulic oil is compressible or not, but a key property of hydraulic fluids is that they must be non-compressible.
‘Non-compressible’ means that the fluid cannot be compressed. Liquids are compressible to some degree, but it is incredibly negligible and not considered for our guide. In contrast, gases are compressible, and so are not used in hydraulics.
Due to the vast array of uses for hydraulic fluid and industrial hydraulic oil, they are used in many applications across every industry.
Here are 10 examples of equipment and machinery which use hydraulic oil:
The properties and characteristics of any hydraulic oil are vitally important to the capability of your hydraulic system to work within the operating conditions you need to use it in. This is especially true of industrial or commercial hydraulic oils.
So, for a hydraulic oil to be useful it needs to have the below properties:
Few, if any, fluids perfectly meet the above criteria. However, there is a comprehensive range of hydraulic oils that specialise in meeting the above properties for the set of conditions in which they are required to operate. Those conditions can range from being required to operate in low temperatures (winter hydraulic oil), high temperatures and a variety of others.
Hydraulic oil is made from a variety of different ingredients, with one base fluid. These ingredients can often be mixed depending on the type of oil you require.
Generally speaking, hydraulic liquids are made up of:
For the varied applications of hydraulic fluid, blenders will mix the base oil with additives of different types to make the properties of hydraulic oil different.
Depending on how you use our hydraulic oil, there will be extra additives which help it perform under different conditions.
Different hydraulic fluid additives include:
These additives are used on their own and together in different blends which are created for different purposes. Hydraulic oil properties can be altered depending on which additives are used, but the typical characteristics tend to be a high viscosity index and be incompressible.
Below is a list of common uses for hydraulic oil and the type of additive/s which may be added to the oil to help it perform at its optimum level.
Hydraulic power is required in some of the coldest places on earth. In these cases, anti-freeze additives are used to prevent the fluid from freezing up or waxing. Low-temperature hydraulic oil is commonly used as a name for fluid which needs to be used in icy conditions.
Under high heat, oil becomes less viscous and flows more easily, which means that it can leak or lose its required properties. Additives are used to retain viscosity for fluids used in applications involving exposure to higher temperatures.
Heavy-duty hydraulic oil is necessary for high-pressure environments where the fluid needs to be able to cope with large amounts of stress. The hydraulic oil additives used here will typically contain anti-wear properties. Anti-wear hydraulic oil is one of the most common blends used in industry and construction.
Biodegradable hydraulic oil is used in applications where an oil spill or leak could potentially contaminate the environment. The typical base oil for biodegradable versions of hydraulic oil includes rapeseed oil and some other vegetable oils.
Environmental hydraulic oil is a strong consideration for those using hydraulic machinery on farms, forests or similar environmentally sensitive sites. This is because the oil is made of a biodegradable base fluid so it will degrade naturally in the event of a spill.
The classifications of hydraulic oil are a subgroup of different fluids with varying performance levels.
Below is a list of common hydraulic oil classifications and their respective descriptions:
For a detailed list, you can speak with our knowledgeable team by calling us on 123 or alternatively, you can read our explainer of hydraulic oil classifications. Find out Crown Oil’s hydraulic oil product specs.
When an additive company sells an additive pack, it will work alongside a particular manufacturer to create a product which works perfectly with that manufacturer’s application. This will be traceable by a hydraulic oil supplier who has used the additive in the fluid. Hydraulic oil ratings or approvals are stipulated by many end users of oil to ensure they’re using the correct fluid for their equipment.
Commonly known as condition monitoring, a hydraulic oil analysis service is used by people who want the most out of their oil before they have to change it in their hydraulic application.
This works by sending a sample of the hydraulic oil to a lab which analyses the sample and reports back with details as to whether it’s good to use further or if it needs to be changed. This gives the end user reassurance that it is still usable and no damage can be done to expensive equipment due to dirty or worn oil.
The importance of oil analysis should be high on anybody’s list.
Below is a list of just a few reasons why it shouldn’t be ignored and how it pays for itself many times over:
Depending on the application of hydraulic fluid, it may be subject to cold or hot temperatures. In some cases, hydraulic oil can be subjected to both hot and cold temperatures which can render the oil useless if it hasn’t been blended with the right additives.
Hydraulic fluids have temperature stability which means they’ll retain their properties within a particular temperature range. Anything above or below this will negatively affect the temperature stability and cause the fluid to either wax and freeze under cold conditions or lose viscosity and potentially leak under hotter temperatures. High heat can cause rapid deterioration of hydraulic oil.
The viscosity of hydraulic oil and temperature is closely linked. As temperature increases, the viscosity of the oil will decrease – a bit like when you put cooking oil in a cold pan it moves slowly but when the pan heats up the oil moves around very quickly and with ease. As the temperature drops hydraulic oil will become more viscous.
Blenders are always trying to make hydraulic oil operate effectively over a wider range of temperatures. This means they’ll go down to low temperatures and still work as effectively as the temperature increases.
To measure the change in viscosity of hydraulic oil when the temperature changes, we use the oil viscosity index (VI). If hydraulic oil has a low viscosity index, a temperature change will alter the viscosity more than if it has a high viscosity index.
Hydraulic oil with a high VI will usually be required in an application which is subjected to a greater range of ambient and/or operating temperatures.
A straight paraffinic mineral base oil will typically produce a fluid with a low viscosity index, whereas a paraffinic mineral base with viscosity improvers will produce a fluid with a high viscosity index.
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The SAE (Society of Automotive Engineers) created a classification table (VI Scale) to show low to high viscosity levels depending on temperature °C. Originally the scale only went up to 100°C but with advances in hydraulic oil blends, the scale now goes above this number!
When it comes to hydraulic oils, viscosity is the measurement of its resistance to flow and it is an important property of hydraulic fluids. This means the fluid will resist compression at different rates depending on its viscosity and take longer to pass through an orifice as the viscosity increases. Hydraulic fluid with high viscosity will be thicker and harder to compress and move as opposed to low viscosity hydraulic oil which will be thinner and pass through easier.
The viscosity of a hydraulic fluid is measured in Centistokes (cSt) and usually at temperatures of 40°C or 100°C. The value will always have the temperature next to it as without this the value will be meaningless. A fluid’s viscosity is measured in a lab using a viscometer as pictured below!
Hydraulic oil viscosity is important for each different application.
The wrong viscosity could cause damage to equipment or have poor results in function.
Please note: This chart should be read horizontally. It assumes 96 VI single-grade oils. The equivalence is in terms of viscosity at 40°C only. Viscosity limits are just approximate; for precise data then you should consult your supplier, ISO, AGMA and SAE specifications. W grades are represented only in terms of approximate 40°C viscosity. For low-temperature limits, consult SAE specifications.
ISO VG – ISO Grade (where ISO is the International Standards Organisation) – the higher the VG number the more viscous the fluid is. The VG number tells you which hydraulic oil is thicker. This is sometimes referred to as the hydraulic oil weight. At the same time, grades with a W next to them indicate the weight (Unlike automobile engine oil which refers to winter oil).
AGMA Grade – American Gear Manufacturers Association are the leaders in the standards of gear oils.
SAE – Society of Automotive Engineers
In the UK, ISO VG is used mainly for grading hydraulic oil. This is a list of common hydraulic oil ISO grades and a general guide to their applications:
Please note that the above examples are just a rough guide and some grades may cross over. It is always best to check with your supplier or manufacturer!
The hydraulic oil flash point is the lowest temperature at which enough vapours are released from the fluid which can be combustible.
Hydraulic fluids play an ever-important part in commercial use, and it’s vital that you source premium quality hydraulic oil from a supplier you can trust.
So, whether you need high-quality hydraulic oil for tractor supply, construction supply or for use in any other industry, we can supply a wide range of hydraulic fluids.
How do you know if you're using the right hydraulic oil? For most lubricated machines, there are plenty of options when it comes to lubricant selection. Just because a machine will run with a particular product doesn't mean that product is optimal for the application.
Most lubricant mis-specifications don't lead to sudden and catastrophic failure, but rather they shorten the average life of the lubricated components and, thus, go unnoticed.
With hydraulics, there are two primary considerations - the viscosity grade and the hydraulic oil type. These specifications are typically determined by the type of hydraulic pump employed in the system, operating temperature and the system's operating pressure. But it doesn't stop there.
Other items for consideration are: base oil type, overall lubricant quality and performance properties. A system's requirements for these items can vary dramatically based on the operating environment, the type of machine for which the unit is employed and many other variables.
Selecting the best product for your system requires that you collect and utilize all available information.
Let me start by outlining the No. 1 lubricant selection criteria: pump design types and their required viscosity grades. There are three major design types of pumps used in hydraulic systems: vane, piston and gear (internal and external). Each of these pump designs are deployed for a certain performance task and operation. Each pump type must be treated on a case-by-case basis for lubricant selection.
Vane: The design of a vane pump is exactly what its name depicts. Inside the pump, there are rotors with slots mounted to a shaft that is spinning eccentrically to a cam ring. As the rotors and vanes spin within the cam ring, the vanes become worn due to the internal contact between the two contacting surfaces.
For this reason, these pumps are typically more expensive to maintain, but they are very good at maintaining steady flow. Vane pumps typically require a viscosity range of 14 to 160 centistokes (cSt) at operating temperatures.
Piston: Piston pumps are your typical, middle-of-the-road hydraulic pump, and are more durable in design and operation than a vane pump. They can produce much higher operating pressures - up to 6,000 psi. The typical viscosity range for piston pumps is 10 to 160 cSt at operating temperatures.
Gear: Gear pumps are typically the most inefficient of the three pump types, but are more agreeable with larger amounts of contamination. Gear pumps operate by pressurizing the fluid between the trapped air volume of the meshing teeth of a gear set and the inside wall of the gear housing, then expelling that fluid. The two main types of gear pumps are internal and external.
Internal gear pumps offer a wide range of viscosity choices, the highest of which can be up to 2,200 cSt. This pump type offers good efficiency and quiet operation, and can produce pressures from 3,000 to 3,500 psi.
External gear pumps are less efficient than their counterpart, but have some advantages. They offer ease of maintenance, steady flow, and are less expensive to buy and repair. As with the internal gear pump, these pumps can produce pressures ranging from 3,000 to 3,500 psi, but their viscosity range is limited to 300 cSt.
Hydraulic fluid has many roles in the smooth operation of a well-balanced and designed system. These roles range from a heat transfer medium, power transfer medium and a lubrication medium.
The chemical makeup of a hydraulic fluid can take many forms when selecting it for specific applications. It can range from full synthetic (to handle drastic temperature and pressure swings and reduce the rate of oxidation) to water-based fluids used in applications where there is a risk of fire and are desired for their high water content.
A full synthetic fluid is a man-made chain of molecules that are precisely arranged to provide excellent fluid stability, lubricity and other performance-enhancing characteristics. These fluids are great choices where high or low temperatures are present and/or high pressures are required. There are some disadvantages to these fluids, including: high cost, toxicity and potential incompatibility with certain seal materials.
A petroleum fluid is a more common fluid, and is made by refining crude to a desired level to achieve better lubricant performance with the addition of additives, which range from anti-wear (AW), rust and oxidation inhibitors (RO), and viscosity index (VI) improvers. These fluids offer a lower cost alternative to synthetics and can be very comparable in performance when certain additive packages are included.
Water-based fluids are the least common of the fluid types. These fluids are typically needed where there is a high probability of fire. They are more expensive than petroleum but less expensive than synthetics. While they offer good fire protection, they do lack wear-protection abilities.
Application should be the most critical attribute when selecting a hydraulic fluid in order to ensure the system's ability to function properly and attain long life. When selecting a hydraulic fluid, it is very critical to determine the system's needs: viscosity, additives, operation, etc.
For example, take a large dump truck that is constantly in the rain, encounters high particle contamination from road debris and leaks 10 percent of its sump volume in two days. There is no need to buy or use the most expensive fluid with the best additive package simply because of the associated cost of replenishment and the inherent lack of maintenance.
On the other hand, you have a very clean, critical and highly loaded system that is maintained properly and used to its full potential. You may want to use a more premium product, such as a highly refined petroleum-based fluid with an AW or RO additive package or even a full synthetic fluid.
As far as the viscosity of the fluid is concerned, this should be determined by the pump type as previously discussed. Not having the correct viscosity for the application will dramatically reduce the average life of the pump and system, thereby directly reducing its reliability and production.
When selecting the appropriate viscosity grade, look for the optimum viscosity required by the pump. This can be determined by collecting data from the pump OEM, actual operating temperature of the pump, and the lubricant properties referenced to the ISO grading system at 40 and 100 degrees Celsius.
Check the operating temperature of the pump and see if it falls between the temperature ranges of the lubricant in question. If not, you may need to increase or decrease the viscosity of the lubricant to achieve the desired, optimum viscosity.
As you can see, selecting the proper hydraulic fluid for the application is not a hard task, but it does require time to research the application, determine the resulting cost and decide which fluid type is best.
You can spend more or less money than is needed simply by not educating yourself on proper lubricant selection techniques. To practice good lubricant selection is to practice great machine performance!
Read more on hydraulic best practices:
How to Combat Leaking Hydraulic Connections
The Seven Most Common Hydraulic Equipment Mistakes
Hydraulic Filter Location Pros and Cons
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